This invention relates to an aircraft wing box construction and, more particularly, the invention is concerned with providing an aircraft wing structure having conventional front and rear main spars along with a plurality of intermediate auxiliary spars canted from the vertical and braced by a plurality of substantially triangular intercostal, spanwise spaced stiffeners. A spar web with one side of the intercostal stiffeners attached thereto is attached at its lower edge to a single spanwise machined spar cap while its upper edge is attached to one of a pair of spaced apart spanwise extended spar caps. The upper edge of the other side of each of the intercostal stiffeners is attached to the other of the pair of upper spar caps.
An airframe wing is essentially two cantilever beams joined together. Each wing tip is the free end of a cantilever, and the center line of the vehicle represents the plane where the two fixed ends of the cantilevers are joined. The prime load-carrying portions of these cantilevers is a box beam made up usually of two or more vertical webs, plus a major portion of the upper and lower skins of the wing, which serve as chords of the beam. This box section also provides torsional strength and rigidity. Normally the prime box is designed to carry all the primary structural loads; these include all beam shears and bending moments, all drag shears and bending moments and the torsional or twisting loads.
At numerous places within the wing box, bulkhead-type structures called ribs are located. These internal structures serve to maintain the rectangular box shape and to cut down the unsupported length of compression cover structures, to separate fuel tanks, and to distribute concentrated loads from guns, bombs, landing gear, or engines into the prime box. They are also located at any wing cross section where major load redistributions occur.
The top of the prime box is the compression chord of the cantilever beam. It is also that portion of the box where the greatest variations in construction are found among the products of various manufacturers. The desirability of minimum weight and the requirements of the various positive and negative bending conditions have produced numerous configurations. In the present invention a series of spanwise continuous extended angle spar caps supported by intercostals and web provide sufficient strength to prevent upper skin buckling up to ultimate design stress while allowing a thinner and lighter upper skin as a result of the increased compression stabilization provided.